Congestive heart failure (CHF), characterized by a progressive enlargement of the heart, particularly the left ventricle, is a major cause of death and disability in the United States and elsewhere. As a patient's heart enlarges, it pumps less efficiently and, in time, the heart becomes so enlarged that it cannot adequately supply blood to the body. The fraction of blood within the left ventricle that is pumped forward at each stroke, commonly referred to as the “ejection fraction”, is typically about sixty percent for a healthy heart. A congestive heart failure patient typically has an ejection fraction of 40% or less, and as a consequence, is chronically fatigued, physically disabled, and burdened with pain and discomfort. Further, as the heart enlarges, heart valves lose the ability to close adequately. An incompetent mitral valve allows regurgitation of blood from the left ventricle back into the left atrium, further reducing the heart's ability to pump blood.
Congestive heart failure can result from a variety of conditions, including viral infections, incompetent heart valves, ischemic conditions in the heart wall, or a combination of these conditions. Prolonged ischemia and occlusion of coronary arteries can result in myocardial tissue in the ventricular wall dying and becoming scar tissue. Once a portion of myocardial tissue dies, that portion no longer contributes to the pumping action of the heart. As the disease progresses, a local area of compromised myocardium can bulge during the heart contractions, further decreasing the heart's ability to pump blood, and further reducing the ejection fraction.
In the early stages of congestive heart failure, drug therapy is presently the most commonly prescribed treatment. Drug therapy typically treats the symptoms of the disease and may slow the progression of the disease, but it does not cure the disease. Presently, the only treatment considered curative for congestive heart disease is heart transplantation, but these procedures are high risk, invasive, and costly. Further, there is a shortage of hearts available for transplant, many patients fail to meet transplant-recipient qualifying criteria.
Much effort has been directed toward the development of surgical and device-based treatments for congestive heart disease. Surgical procedures have been developed to dissect and remove weakened portions of the ventricular wall in order to reduce heart volume. As is the case with heart transplant, these procedures are invasive, risky, and costly, and many patients do not qualify medically for the procedure. Other efforts to treat CHF include the use of an elastic support placed around the heart to prevent further deleterious remodeling, and mechanical assist devices and completely mechanical hearts have been developed. Recently, improvements have been made in treating patients with CHF by implanting pacing leads in both sides of the heart in order to coordinate the contraction of both ventricles of the heart. While these various procedures and devices have been found to be successful in providing some relief from CHF symptoms and in slowing disease progression, none has been able to stop the course of the disease.